index.jscontains the root node we create and mentions the
documentvariable. There will be little to no changes to this file while writing the app, except maybe to
importanother Sass file.
App.jsxcontains the React app. This structure is to enable Fast Refresh (described below) but is also to completely separate the code mentioning the
documentvariable from the actual React code for modularity.
watchcommand to run Webpack, and have integrated watch functionality into Express. In
index.mjswe detect that we are in the
developmentenvironment and start the Webpack watcher from within Express. This means we can run both Express and Webpack simultaneously in watch mode with